1. Field of the Invention
This invention relates to differential disconnect drive assemblies or mechanisms, and in particular to dual disconnect drive assemblies, for tandem and multi-axle vehicles which can be quickly and easily engaged and disengaged as required.
2. Description of Related Art
Four-wheel drive vehicles, which are operable in either a two-wheel drive mode or a four-wheel drive mode, have gained widespread popularity. Axle disconnect mechanisms, or differential disconnect mechanisms or assemblies for such vehicles are known.
Commonly used disconnect mechanisms for four-wheel drive vehicles disconnect only one of the two output shafts on an axle assembly which is driven part time. This causes the pinion gears and the side gears of the differential to rotate due to back driving, although the differential case remains stationary. This is not compatible with speed-sensitive limited slip differentials. Also, single axle disconnect mechanisms may cause noise and wear and poor fuel economy due to rotation of the differential components while the vehicle is in two-wheel drive mode.
Various dual disconnect differential assemblies or mechanisms have been proposed. These mechanisms in general have an unnecessary number of moving parts, are fairly complex, and would be suitable only for installation on relatively wide vehicles because of the space required. Earlier designs have interposed a clutch member between the side gear and the axle shaft. None has achieved desirable commercial acceptance.
For tandem or multi-axle vehicles, current systems typically uncouple the input (prop) shaft when an axle is not needed to propel the vehicle (e.g., on highway use). This technique forces the ring gear and differential to rotate even when torque is not being transmitted through the drive axle assembly. This unnecessary rotation causes unwanted wear and frictional losses.
The need exists for a system that allows the ring gear and differential gears to remain stationary when the axle is disengaged.